I am travelling to Sri Lanka this Saturday for a couple of weeks.I like to visit one or two forest monasteries there, but I can't find any information about forest monasteries in Sri Lanka...Could anyone point me to some online resources, or maybe a list of addresses?

I think you are in the wrong section. If you check "Ordination and Monastic Life" under "Modern Theravada" section (viewforum.php?f=30) there are already several threads on the same question by other members.